1. Field of the Invention
The present invention relates to equipment for fabricating partitioning ribs of a plasma display device and, more particularly, to equipment for fabricating partitioning ribs by ejecting partitioning rib grains to form partitioning ribs.
2. Description of the Related Art
In recent years, flat panel displays have attracted attention as display devices that can achieve space saving instead of CRTs (cathode-ray tubes) that have been widely used heretofore.
Various types of flat panel displays of this kind are available such as liquid-crystal displays (LCDS), plasma display panels (PDPS), field emission displays (FEDS), organic EL displays (ELs), and light-emitting diodes (LEDs). They are used separately according to application. Today the LCD enjoys the most widespread acceptance.
Larger screen areas and wide viewing angles can be more easily imparted to plasma display devices than the LCD described above. For these and other advantages, the plasma display device is one of devices that attract the greatest attention in the field of large-sized displays providing full color display.
Such a plasma display device is fabricated by forming a number of elongated data electrodes on a back substrate consisting of a glass plate or the like, forming partitioning ribs in the form of stripes on the opposite sides of the data electrodes, and forming a phosphor layer in the cells surrounded by the partitioning ribs.
Then, a number of elongated bus electrodes and transparent electrodes are placed vertical to the data electrodes. A front plate is placed from above to cover these electrodes. A mixture gas of rare gases such as He, Ne, and Xe is sealed into the discharge gas spaces surrounded by the partitioning ribs.
When a display is provided by such a plasma display device, if an AC pulse is applied between adjacent transparent electrodes, a gas discharge is produced, creating plasma inside the discharge gas spaces. The resulting ultraviolet radiation excites the phosphors, giving rise to visible light.
The aforementioned partitioning ribs are formed like stripes in the case of the AC type PDP. In the case of the DC type PDP, partitioning ribs are formed like cells.
The partitioning ribs are formed on the aforementioned glass plate or panel by some means described below but all of these means suffer from problems associated with read time and accuracy:
(1) Lift-off method (photoengraving): Read time is 135 minutes. The rib width cannot be thinned greatly.
(2) photosensitive paste method (photo-insulator method): Read time is 113 to 333 minutes. It is impossible to reduce the rib width greatly. Furthermore, the accuracy of the rib height is not very good.
(3) photosensitive film method: Read time is 135 minutes. The rib width cannot be reduced greatly.
(4) Sandblasting: Read time is 58 to 142 minutes. It is impossible to reduce the rib width greatly.
(5) Screen printing method: Read time is 128 to 192 minutes. The rib width cannot be reduced greatly. In addition, the accuracy of the rib height is not very good.
(6) Pressure molding: Read time is as short as 17 minutes. Ribs can be processed accurately. However, molding equipment is necessary.
Currently, screen printing and photolithography are predominant and will be hereinafter described in detail. In either case, the formed partitioning ribs cannot be shaped into an ideal cross-sectional shape in accordance with an embodiment of the present invention, the embodiment being described in connection with FIGS. 13 and 14.
Screen printing is used to print a partitioning rib pattern on a glass plate or panel by means similar to printing, using a mesh screen made of a metal or resin. A process consisting of this printing and drying is repeated about 10 times to form partitioning ribs about 1 mm tall. Finally, they are sintered. This method has the advantage that undesired wasteful material is not produced. However, the shape and the dimensions of the partitioning ribs cannot be fabricated accurately. Furthermore, the mesh is elongated, requiring frequent exchange. In this way, various difficulties occur. In addition, high accuracy cannot be secured unless the screen length is about three times the length of the printed pattern and so the equipment is made huge.
On the other hand, photolithography consists of printing a thick-film paste uniformly over the whole glass plate, sintering the paste, applying a photoresist, stacking photomasks having burn-in patterns over each other, and developing the photomasks. The developed burn-in patterns are etched away. Also, with this method, the process consisting of printing, drying, and exposure is repeated about 10 times. Finally, sintering is done. This method can form partitioning ribs with better shapes and accuracy than the aforementioned screen printing. However, it must be said that this method still has drawbacks. Furthermore, production process results in a large amount of wasted materials. Hence, the method is wasteful. From a viewpoint of equipment, considerable production space is necessary because exposure system and development (etching) system must be added to the above-described screen printing system.
After forming the partitioning ribs described above, phosphors are applied. Some methods are available to apply the phosphors. Today, the main means for applying the phosphors are screen printing and photolithography.
In the former screen printing, one plate is fed in steps corresponding to colors of R, G, and B. Thus, the various colors are printed. This method has the advantage that the process sequence is simple and the phosphor materials produce only small amounts of loss. However, the method presents some problems, e.g., sufficient dimensional accuracy cannot be obtained, and mixing of colors results.
In the latter photolithography, the process sequence consisting of printing, exposure, and development is repeated three times for the three colors of R, G, and B. This method can provide somewhat higher accuracy than the screen printing. However, the process sequence is complicated and so considerable production space is necessitated. Furthermore, this method has some drawbacks such as production of large amounts of loss of materials.
Specific examples of techniques associated with application of the phosphors and formation of the partitioning ribs are as follows.
For example, Japanese Patent Publication No. 2679036 describes a technique for applying phosphors to form partitioning ribs by ink jet technology. The technique described in this Patent Publication is intended to cause phosphor materials to adhere to the exposed surface of the substrate that is at the deepest locations around the partitioning ribs.
The technique for applying phosphors as described in this Patent Publication No. 2679036 provides a process step different from the step for forming partitioning ribs. Therefore, this technique does not contribute to improvement of the production efficiency. Furthermore, the phosphors are not applied to the surfaces of the partitioning ribs but to the substrate at the deepest locations around the partitioning ribs.
Japanese Patent Publication No. 2716013 describes a technique for forming grooves in a glass plate or substrate whose surface has been blackened to form partitioning ribs between the grooves. Since insulator layers can be omitted, the structure and the production method are simplified.
However, in the technique described in this Patent Publication No. 2716013, it is necessary to process glass accurately. Hence, it is difficult to form partitioning ribs of ideal shape.
In any of the techniques described in the above-cited Patent Publications, partitioning rib material is not ejected from nozzle members.to form partitioning ribs.
In the above-described conventional techniques, it is impossible to fabricate partitioning ribs having accurate shape and dimensions with relatively small-sized production equipment. Consequently, there is a demand for techniques achieving this.
It is an object of the present invention to provide equipment for fabricating plasma display panel (PDP) partitioning ribs with accurate shapes and dimensions with relatively small-sized equipment.
In summary, this invention provides equipment for fabricating partitioning ribs for a plasma display panel or device. This equipment includes heads having nozzle members for ejecting partitioning rib grains to form the partitioning ribs.
This object and advantages of the invention will become apparent from the following detailed description.